1. Field of the Invention
The present invention pertains to common rail fuel injection control and particularly relates to the improvement and the like of the reliability of a system resulting from the protection of injectors.
2. Description of the Related Art
Conventionally, as this type of system, a common rail fuel injection system that is configured to pressure-feed high pressure fuel to a common rail by a high pressure pump, supply the high pressure fuel that has been pressure-accumulated in the common rail to injectors that are disposed in correspondence to cylinders, and inject the high pressure fuel at a predetermined timing to the corresponding cylinders of an internal combustion engine from each of the injectors is disclosed in JP-A-2003-278586 and the like and is well known.
In this common rail fuel injection system, it is normal to return excess fuel inside the injectors to a fuel tank after injection, and that kind of configuration is employed even in the conventional system disclosed in the aforementioned published application and the like.
However, the excess fuel in the injectors that has not been used in injection as mentioned above obtains thermal energy and reaches a high temperature state because of pressure fluctuation resulting from a sudden drop in pressure after injection inside the injectors. Normally, as for injector head portions, the disposed positions and the like of the injectors is considered such that the excess fuel temperature does not rise above a constant by air cooling resulting from traveling wind or the like. However, realistically, although it is extremely difficult to assume the occurrence of a situation where air cooling by traveling wind or the like becomes insufficient for whatever reason and the flow of the wind temporarily ceases, it cannot be said for sure that the occurrence of such a situation is theoretically nonexistent.
Additionally, in that kind of state, when return of the excess fuel such as mentioned previously is performed, it is conceivable for this to lead to an abnormal rise in the fuel temperature and for there to be a drop in the function of the injectors; therefore, it is theoretically conceivable for this to lead to a situation where vehicle operation stops, and from the standpoint of further improvement of the safety and the reliability of the vehicle, it is preferable to take coping measures that will be sufficient even in a situation where the potential for this theoretical occurrence is predicted, and a vehicle with higher safety and higher reliability is desired.
Incidentally, in the conventional system disclosed in the previous published application, a measure is disclosed which, when a temperature of the injectors that exceeds a predetermined value is detected, suppresses an excessive rise in the injector temperature, improves the thermal reliability of the system and therefore prevents a decrease in the injection amount and a drop in the output resulting from an excessive rise in the injector temperature by controlling an energizing electric current to the injectors and the like.
This measure is capable of becoming one means for solving the aforementioned problem in that the measure suppresses a rise in the injector temperature, but it is necessary to newly dispose a sensor that detects the temperature of the injectors, and in a vehicle where simplification of the configuration and a reduction in the number of parts and the like are required as much as possible, the addition of new parts, such as even one sensor, is decidedly not expedient.
Given this, there is desired a measure that can reliably prevent a drop in the function of the injectors resulting from a rise in the temperature of the excess fuel and improves the reliability of the system without having to add a new part and without having to directly detect the temperature of the injectors.